Seekins Precision SP223, Gen2, Semi-Automatic, Billet Lower Receiver, 223 Rem, Black Finish, Enhanced Bolt Catch, Tensioning Screw, Ambi-bolt Stop 0011000008 Precision CNC machined from solid billet aluminum, the SP223 Billet Lower is the best AR lower receiver available. Far exceeding Mil-Spec requirements, the SP 223 has features not found on standard lowers such as the Seekins Precision Enhanced Bolt Catch, receiver tensioning screw, ambi-bolt stop assembly and an oversized trigger guard. These features combined with superior fit and finish make the SP223 the perfect foundation for any AR build.